Having read in a recent Island Connections that anyone who bought a prepaid mobile/sim card before 2007 (which is me) must register their name and address with their provider or their number will be cancelled and returned
to the telephone company for redistribution at the end of October 2009.
This is alledgedly said to help prevent terrorist activities.
Many swallows/sparrows (well they go cheap, cheap most of the time) hold Spanish Sim cards which they use only whilst wintering on the island.
Those affected need to take a copy of their identity docs and proof of your regular Spanish address and passport to your operator.